Preheat oven to 400˚F.
Slice off the top of the head of garlic, exposing the cloves.
Place the leeks, cauliflower, broccoli, zucchini, potatoes and garlic on a large sheet pan. Drizzle with olive oil, 1 teaspoon salt and pepper and toss gently. Roast for 30 minutes, until all vegetables are fork tender.
About 10 minutes before the vegetables are done, add the broth and peas to a small pot and heat until simmering.
Add all of the vegetables (only add half of the garlic cloves) to a blender, along with the hot broth + peas, lemon juice, spinach, parsley, remaining ½-1 teaspoon salt (this depends on your preference and type of salt used) and red pepper flakes and blend until smooth.
